1. Field of the Invention
The present invention relates to a thermal transfer recording device which transfers an image on a recording sheet using an ink film coated with sublimation ink or the like.
2. Description of the Related Arts
In conventional thermal transfer recording devices, thermal heads press through an ink film so as to make pressure contact with a recording sheet disposed against a platen roller, thereby reproducing an image on the recording sheet. Particularly when reproducing a color image on a recording sheet, an ink film coated with three ink colors of, for example, yellow, magenta and cyan is used to print the image on the recording sheet by sequential overlays of the image in the different colors. The aforesaid type of thermal transfer recording device is said to use a return printing method or planar sequence method wherein a monocolor image is printed first, followed by the recording sheet being transported back to the original position for the printing of an image in a second color. Three color printing is accomplished by substantially the same process.
The previously described type of recording device can reproduce color images on various kinds of recording sheets made of dissimilar materials such as a plain paper, transparency sheet for overhead projectors (OHP) and the like. However, in the following description an ink film is used.
The optimum energy applied to the thermal head is standardly set for plain paper. The aforesaid optimum energy induces a reduction in the print quality level relative t print density and the like when reproducing color images on OHP sheets using the same ink film.
Thermal recording devices have been proposed which have various functions for discriminating the different types of recording sheets and which apply an energy on the thermal heads that corresponds to the discriminated type of recording sheet in order to prevent the previously described reduction in the level of print quality.
However, even if the aforesaid applied energy is changed when reproducing a color image using the same ink film, there are limits to the degree to which deterioration of print level quality can be prevented.
In recent years, ink films have been proposed which are coated or the like with inks optimally suited for paper quality recording sheets. Accordingly, the level of print quality can be improved to produce superior color images by loading in the thermal recording device an ink film compatible with the type of recording sheet to be used.
Preventable reduction in print quality in the previously described instance is achievable when the type of recording sheet and the type of ink film are compatible, but is not preventable when the recording sheet and the ink film types are not compatible. Thermal transfer recording devices using ink film coated with sublimation ink not only exhibits a deterioration in print quality when images are reproduced using incompatible recording sheets and ink films, but also have the disadvantage of wasting relatively expensive recording medium.